The present invention relates to wiper blades for windows of motor vehicles.
In wiper blades the support element is meant to assure the evenest possible distribution of the wiper blade contact pressure on the windows, over the entire swept field swept by the wiper blade. By means of a suitable curvature of the unstressed support element—that is, when the wiper blade is not applied to the wiper blade—the ends of the wiper strip, which in wiper blade operation is pressed entirely against the window, are urged toward the window by the then-stressed support element, even if the radii of curvature of spherically curved vehicle windows differ in every position of the wiper blade. The curvature of the wiper blade must accordingly be somewhat greater than the greatest curvature measured in the swept field of the window to be wiped. The support element thus replaces the complicated support bracket construction, having two spring rails disposed in the wiper strip, of the kind employed in conventional wiper blades (German Published, Unexamined Patent Application DE-OS 15 05 397).
In a known wiper blade of this type (German Patent DE-PS 12 47 161), the wiper blade, or its support element, which for reasons of distributing the contact pressure protrudes far past the wiper strip in the middle region of the wiper blade, can on the one hand be engaged from below, on the front side facing into the wind, with an attendant buildup of overpressure, by this overpressure. On the other hand, on the back side facing away from the wind, because of the structural form noted above, a considerable negative pressure builds up. Although the wiper blade, which during operation usually executes a pendulum motion, constantly changes its position relative to the oncoming relative wind, even then one of its long sides is always more or less greatly exposed to the wind and is therefore called the front side, while its other long side is accordingly also thought of as the back side. At relatively high vehicle speeds, given the cooperation of these two aforementioned pressures, both of which are oriented counter to the wiper blade contact pressure, this contact pressure is reduced at least enough that proper wiping is no longer possible. Increasing the wiper blade contact pressure against the window at high vehicle speeds could admittedly reduce the severity of this problem, but at lower vehicle speeds, when the liftoff tendency is less, the friction between the wiper blade and the window increases; this leads to undesirable noise buildup and to excessively high stress on the drive components and on the rubber of the wiper.